(57) An apparatus and method for supplying a polyphase (AC) alternating current motor
(15) with driving voltages. A conversion unit (12) is coupled to phases of the polyphase
AC motor and includes a plurality of switching devices and includes, in at least one
phase, a first switching device (25b,26b,27b) between a bus (24) of an AC power supply
and an output terminal, a second switching device (21b,22b,23b) between a bus (16)
of a direct current (DC) power supply and the output terminal, and a third switching
device (18a,18b,19a,19b,20a,20b) between a common bus (17) for the AC power supply
and the DC power supply and the output terminal. Driving voltages for the polyphase
AC motor are generated by selecting a voltage from among voltages having potential
values corresponding to the AC power supply and the DC power supply, and the selected
voltage is used to operate a switch of the plurality of switching devices.
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